1. Field of the Invention
The present invention relates to the process step of dewatering aqueously slurried, solid waste treatment sludge. More particularly, the present invention relates to a process and apparatus for monitoring the combination of flocculation chemical with an aqueous sludge influent stream to a dewatering press apparatus.
2. Description of the Prior Art
Aqueous sludge is the product of such diverse processes as municipal and industrial waste treatment, fly ash control and fuel coal preparation. In substance, such sludge comprises an aqueous mixture and suspension of finely divided particulate solids: some of which are hydrated and/or electrostatically charged. In the interest of environmental protection and economic material handling, these particulate solids must be separated from the aqueous vehicle prior to recycle or release. Traditional mechanical screening is inadequate due to the hydrated nature of the solids or the extremely fine particle size. Although a large percentage of the particulates would, in time, dewater gravimetrically, high throughput volume demands on most processing facilities would require exorbitantly large process equipment to implement gravity separation. Accordingly, other means and devices are frequently used to condition the sludge for accelerated dewatering.
One of the more successful sludge conditioning devices is the addition of chemicals which promote particulate dehydration and coagulation. These chemicals are known generically to the industry as flocculants. Common examples of sludge flocculation chemicals include ferric chloride, calcium chloride, sulfuric acid, starch, lime, alum and snythetic polymers of an anionic, cationic or nonionic charge nature. Flocculant is blended with the sludge influent stream to a mechanical screening device such as belt filter press.
By most standards, flocculants are relatively expensive chemicals. Due to the consumption quantity necessary for a large waste water treatment plant, therefore, flocculant may represent the greatest single element of cost to the plant operation. Moreover, the rate of flocculant addition is not a fixed function of the sludge volume throughput. Many factors variable to the sludge constituency continuously alter the flocculant demand. Consequently, continuous operator attention to the screening equipment is required for manual evaluation and adjustment of the flocculant flow rate. Central to the operator's evaluation process is the sludge cake or consistency upon filter press entry. A fluidized sludge at that point denotes insufficient flocculant whereas a stiff and crumbling sludge cake suggests an excess of flocculant, and hence, waste. A factor of 2 may represent the difference between an adequate flocculant flow rate and an excessive flow rate. Because of plant housekeeping chores incident to an inadequate flocculant flow rate, however, operators have a natural tendency to overdose the sludge influent.
It is, therefore, an object of the present invention to provide an automatic method and apparatus for evaluating sludge flocculant flow rate and adjusting the rate correspondingly.
Another object of the invention is to provide a method and apparatus for evaluating the consistency of sludge cake upon belt filter press entry.
Another object of the invention is to provide a sludge cake surface sensor signal analysis method to infer a corresponding cake consistency and flocculant adequacy.
Another invention objective is to provide an abnormal operation monitor to initiate alarms and subsystem shutdowns in the event of certain equipment or sludge supply failures.